A great variety of pathogenic microorganisms such as bacteria and fungi are causative agents in producing diseases in man, animals and plants. Although a number of antibiotics have been developed, some of which possess usefully high antimicrobial activity against one or more pathogenic microorganisms, there remains a need for more effective therapeutic agents to combat the many diseases caused by such pathogenic microoganisms in man, animals and plants.
An object of this invention is to provide new antibiotics which are useful as antibacterial agents for therapeutic treatment of bacterial infections in man and animals and/or for sterilization of surgical materials and instruments. A further object of this invention is to provide a process for the fermentative production of these new antibiotics. Other objects of this invention will be clear from the following descriptions.
We have done extensive research in an attempt to produce and obtain new and useful antibiotics. As a result, we have now found that when a new strain of the genus Streptomyces which was isolated from a soil sample collected at sea bottom in the coast of the Miura Peninsula in Kanagawa Prefecture, Japan and which was alloted a laboratory designation, Strain No. SS-939 is cultivated in a culture medium under aerobic conditions, four different substances having antibacterial activity against a wide variety of bacteria are produced and accumulated in the culture. We have succeeded in isolating these antibacterial substances from the culture and purifying them. From the chemical, physical and microbiological studies of these isolated substances, it has been confirmed that each of these isolated substances is a new aminoglycosidic antibiotic which has low toxicity and which is distinguishable from any of the known antibiotics. Thus, we have denominated these four new antibiotics as istamycin A, istamycin B, istamycin A.sub.o and istamycin B.sub.o, respectively.